1. Technical Field
The present invention relates to an image processing apparatus, and in particular, to a halftoning technique.
2. Background Technology
Halftoning techniques are known in image processing apparatuses which are provided with a printing function such as printers, facsimiles, copiers, multifunctional printers, or the like. In halftoning, input gradation values are converted into output gradation values as a signal which controls the size of ink droplets or a signal which controls the pulse width of a laser which forms a latent image on a photosensitive body. Since the number of gradations in the output gradation values is lower than the number of gradations in the input gradation values, a number of gradations which is higher than the number of gradations in the output gradation values is approximately expressed by using a continuous region with a predetermined area. For example, it is possible to approximately express a number of gradations which is higher than the number of gradations which are output for each dot by using different conversion patterns from the input gradation values to the output gradation values for each of the coordinates inside the continuous region with the predetermined area as described in Patent Document 1 and Patent Document 2.
Japanese Laid-open Patent Publication No. 2002-369001 (Patent Document 1) and Japanese Laid-open Patent Publication No. 2003-162717 (Patent Document 2) are examples of the related art.